The Hall Effect SensorRene Dupuis

Background InformationThe Hall effect was discovered by Edwin Hall in 1879; electron was not experimentally discovered; had to wait until quantum mechanics came Development of semiconductor compounds in 1950's led to first useful Hall effect magnetic instrumentIn the 1960's, first combinations of Hall elements and integrated amplifiers Resulted to classic digital output Hall switchIn 1965, first low-cost solid state sensor

Theory of the Hall EffectHall effect principle, no magnetic fieldHall effect principle, magnetic field presentPotential Difference (voltage) across output:V = I * B

Basic Hall Effect SensorHall element is the basic magnetic field sensorDifferential Amplifier amplifies the potential difference (Hall voltage)Regulator holds current value so that the output of the sensor only reflects the intensity of the magnetic field

BOP Operate point A positive magnetic field > BOP will switch the sensor on (output low). BRP Release pointRemoval of the magnetic field < BRP will switch the sensor off (output high). Bhys HysteresisUnipolarLatchingBipolar

TypesMagnetic Parameters

UnipolarRequires single polarity magnetic field for operationPositive magnetic field (South pole) Directed towards branded face of the sensor for activationTrue-Power-On StateBRP

LatchingRequire both positive and negative magnetic fieldsSymmetrical Duty Cycle operationGuaranteed power-up state>BOP or

BipolarInvolves either Unipolar or Latching characteristicsSame principle

Unipolar ModeLatching Mode

Sensor switch operationPower-up states

Hall Effect Sensor Example

Application: Response to South or North PolarityMotor-Tachometer application where each rotation of the motor shaft is to be detected

When ring magnet rotates w/ motor, South Pole passes the sensing face of the Hall sensor after each revolution.

Sensor Actuated when the South Pole approaches sensorDeactuated when South Pole moves away from sensor

Single digital pulse produced for each revolution.

Application: Gear Tooth Sensing Sensor detects change in flux level Translates it into a change in the sensor output (high to low) Sense movement of ferrous metal targets (magnetically biased)

BenefitsSmall and rugged non-contact sensors Insensitive to oil, dirt, humidity and dust High magnetic sensitivity Accurate and Reliable Delivers low Power consumptionSupply voltage capability Average current consumption

Prices and SourcesRange from $1-$60

Allied ElectronicsAllegromicro Digi-Key

SensorIndicates Direction Output Rotational or Linear Notes Optical Incremental EncodersYesDigital (Quadrature) Both Uses light and optics to sense motionInterruptersNoDigital (SinglePulse) RotationalSenses light with light beam interruptPhoto-reflective sensorsNoDigital (SinglePulse)LinearGenerates pulse whenever sensor receives reflected light Laser InterferometerYes Digital (Quadrature)LinearLaser supply linear displacement of an objectTriangulation SensorsYesAnalogLinearLaser supply non-contact linear displacement of an objectHall-Effect SensorsNoDigital (SinglePulse)Rotational

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